Method of recovering hydrocarbons from an underground hydrocarbon containing formation

ABSTRACT

An improved method for oil recovery from a formation using a combination of steam and in situ combustion drives comprising injecting steam via an injection well, followed by injecting a combustible gas via a production well and thereafter recovering oil via the injection well.

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority Robert W. Zwicky Alberta, Canada 807,196

Mar. 14, 1969 Feb. I6, 1971 Shell Oil Company New York, N.Y. Feb. 2l, 1969 Canada METHOD 0F RECOVERING HYDROCARBONS FROM AN UNDERGROUND HYDROCARBON CONTAINING FORMATION 2 Claims, 2 Drawing Figs.

U.S. Cl. 166/261, j l66/263, 166/272 Int. Cyl. E21b 43/24 [50] Field of Search 166/272, 302,l 303, 263, 25l, 252, 256

[56] References Cited UNITED STATES PATENTS 3,379,246 4/1968 Sklar et al 166/251 3,384, l 72 5/1968 Hujsak et al. l66/272 3,4l 1,575 ll/l968 Connally, Jr. l66/263X 3,460,621 8/1969 Gum et al` l66/263 3,476,183 ll/l969 Haynes, Jr. et al l66/272 Primary Examiner-Stephen J. Novosad Attorneys-G. G. Pritzker and J. H. McCarthy ABSTRACT: An improved method for oil recovery from a formation using a combination of steam and in situ combustion drives comprising injecting steam via an injection well, followed by injecting a combustible gas via a production well and thereafter recovering oil via the injection well.

PAENEn sa 1 s 191| FIG. 2 INVENTORI ROBERT W. ZWICKY BY: 1MM

HIS AGENT METIIOD or RIacovI-:IuNol IIYDROcARIIONs FROM AN UNDERGROUND ItYDROcARnON coNrAININc iFORMATION BACKGROUND OE'THEINVENTION the drainage of these hydrocarbons so as to facilitate oil recovery. I j c The heat required for the desired viscosity reduction ofthe hydrocarbon can be generated in situ by injecting oxygen-,containing gas into the pores of the formation, which gas causes combustion of part of the hydrocarbon present within the formation. The water vapor generated during this reaction condenses against the cold parts of the formation, thereby forming a condensation front which heats the hydrocarbon .and drives it towards the production'wells; A` drawback of this method is the high cost of compressing the oxygen-containingl gas to a suitable pressure beforeinjejcting it into the formation. ln` another thermal method," `a 4hot fluid such as hot water, steam or another condensible gas is injected into the pores of the formation. The hot fluids heats the` hydrocarbon and then displaces the hydrocarbonthrough the pores ofthe formation to the production wells. In this method, thefcost involved per unit of enthalpy supplied to the formation is less than the cost involved in `the above-mentionedin situ combustion method. A drawback of this method, however, is the loss of heat to the part of the formation being treated, as well as the loss` of heat to the cap rock and the base rock,` which losses may become unacceptable near the endof theloperatio'n, iniparticular if there are great distances between the individual wells. Still another method of thermal oil recovery comprises injecting into `a formation from which oil is to be recovered via an injection well a hot fluid followed b y injectingthrough the same well an oxygen-containingg'asin order to establish a combustion front so as to drive oil to a production well to recover oilY therefrom. However, in this process the` oil recovery path established by this system and fluid flow-is difficult to control thus decreasing 'the efficiency of oil recovery.

. EMBODIMENT OETIIE INVENTION ln accordance with thev present invention these disadvantages of the known methodsa'are reduced or eliminated,

vand a high recovery of hydrocarbons from a hydrocarbon-containing underground formation can be achieved at relatively low compression costs and with relatively low heat losses.

According to the invention the method of recovering hydrocarbons from an underground, hydrocarbon-containing formation comprises the following steps l. arranging at least two wells penetrating into the formation and communicating with the pores of the formation,

2. injecting via one or more of the` injection wells into the pores of the formation unsaturated, ysaturated or supersaturated steam into the unheated parts'of the formation under the conditions of operation, until a portion of the hydrocarbon has been mobilized or fluidized,

3. after the cessation of such injection, injecting via one or more production wells `an oxygencontaining gasV so as to create an in situ combustion front, and t v 4. recovering hydrocarbon alternately through the produc- It is also preferred that the steam injection in step 2 is injected at the lowest practical pressure. The water that is formed by steam condensation during the steam injection step aids in controlling the later in`situ combustion resulting from `the oxygen-containing gas (air) injection, as well as total heat utilization. v j

The invention will now be described, by way of example, with reference tothe accompanying drawing, which show schematically a vertical section of part of the earths crust including a hydrocarbon-containing formation, and injection and production wells. In this formation, the mobility of the hydrocarbonpresent in the pores is sufficiently low that it cannot be recovered in the most economic manner under influence of its own energy or by the aid of pumping equipment `installed in the wells. The mobility is', furthermore, sufficiently low that the application of a coldflluid drive is not economically feasible. Such hydrocarbon has hitherto only been economically recoverable, if at all, bya thermal method.

DEscRII'rION OE THE FIGURES ln FlGS.l and 2 from the Ysurface l0 and through the layers 1l and l16 overlying the hydrocarbon-containing formation `l2, there are drilled two wells I3 and 14, which penetrate into the formation 121. .The wells are drilled and completed in a manner known per se, and for sake of simplicity all details such as casing, tubing, wellhead, cementing layers, liners, etc. are omitted from the drawing and description. One of the wells I3, is designed as an injection well for injecting steam for heating the contentsof the formation 12 and from which Oil is to be recovered via tubing string I8. The other well, I4, is designed` as a production well from which oil is to be recoveredvia tubing string 2I'anjd via which a combustible gas, e.g., air is injected to establish in situ combustion.

tially horizontal, it Vwill be understood that the method of the invention may be applied with similar results to hydrocarboncontaining formations which are of the slanted type. The cap rock 16 which formspart of the overlying layers with Il as well as the base rock I7, are substantially or entirely impermetion well(s),` and then the injection well(s) during the sequence v levelnear the lowest part of the formation.

able. v

SPECIFIC DESCRIPTION OE THE EMBODIMENT OF THIS INVENTION ln accordance with thev invention, there is first injected steam via injection well 13 via valved line 22 into the pores of the formation .as shown in FIG. l. This steam may be either wet, dry or superheated. If desired?, a hydrocarbon may be mixed with the steam for increasing the recovery efficiency.

The injectivity of the steam into the formation l2 may be increased in the neighborhood lof the well I3, by any of the methods known in the art.

The steam is obtained from any convenient source (not shown), and must of course beat a pressure higher than the formation pore pressure, this steam is vconducted under this pressure into the' top of the .well ll3 via valved line 22. lf desired, bleedwater from a boiler supplying the steam may also be injected into the well I3. This has the advantage that salts concentrated in the residue waiter are removed from the boiler without loss of heat. Thesewill be removed from the boiler. if wet steam is employed for injection. The injection of steam into the formation l2 is stopped after at least 50 percent of the pore volume of the part of the formation to be treated has been heated. This means in practice that the amount of injected steam is more than 0.5 to 2 times the pore volume measured as steam condensate. It is to be understood that the part of the formation treated is that part of During injection of the steam, condensation occurs against the relatively cold hydrocarbon forming a condensation front 19 which, under the influence of further steam injection, travels in the direction of the production well 14, with the aid of pumps or the like. All of the formation between the injection well 13 and condensation front 19 has been treated and much of the hydrocarbon therein swept out to the production well 14. lt is not necessary to the practice of this invention that the full vertical section of formation l2 be swept by the condensation front 19 during this step.

After the desired amount of steam has been injected into the pores of the formation l2, this injection is stopped, and in place thereof compressed air or other oxygen-containing gas such as air is pumped into the pore space of the formation 12 via production well 14 through valved line 23 where the temperature conditions enable spontaneous combustion to take place wherever the oxygen-containing gas comes into contact with sufficiently great amounts of hot hydrocarbon. ln this way, as shown in FlG. 2, a combustion front 20 is formed, which travels in the direction of the injection well 13, and by virtue of vaporization and subsequent condensation of water already present in the formation and of water created by the combustion also forms a condensation front 24 which travels ahead of the combustion front 20 towards the injection well 13. Hydrocarbons are heated by the condensation of steam to water and are mobilized, then caused to flow to the injection well 13 through the heated and depleted path 25 established during the steam injection step. A v

The present process encompasses a bidirectional injection scheme whereby steam drive between well 13 and well 14 is alternated with forward combustion between well I4 and well 13 after steam drive from well 13 to well 14. On the other hand, the process described in U.S. Pat. No. 3,409,077 provides for cyclic steam drive/forward combustion with both steam and air injection conducted in one direction only. The advantages of the present invention is that there is always provided during the combustion phase a well developed heated and depleted path through which the mobilized hydrocarbons, e.g., tar can move. This is a better path than that developed in a monodirectional system as described in the art mentioned above as the depletion and heating is most intense at the combustion phase production well. The bidirectional system of the present invention thus gives added assurance that fluid flow retardation through cooling of the hydrocarbons. e.g.. tar will not occur. The second advantage of the present process is that air is injected towards the main heated area rather than through this area. This method assures that air Acontacts tar or other hydrocarbons at the outer edge of the heated zone and combustion occurs at the point where the heat can be most beneficial. Most of the oxygen available for combustion is consumed at that point, any remaining oxygen is reacted with residual tar in the heated zone thus avoiding hazardous oxygen breakthrough into the production well. Where the hydrocar bon is sufficiently viscous, several alternate passes" of steam and combustion to and from a particular well may be required until the heat has risen to the top ofthe formation.

Although in the example described with reference to the drawing only two wells have been shown for carrying out the method according to the invention, the present invention is by no means limited thereto. Any number of wells and any type of well pattern may be used.

l. Method of recovering hydrocarbon from an underground hydrocarbon-containing earth formation containing hydrocarbon in a substantially nonmobile state at ambient temperature. consisting essentially of the following steps:

l. arranging at least two wells of which one is an injection wel! and one is a production well penetrating into said formation and communicating with the pores thereof;

2. injecting steam through one of the injection wells into the pores ofthe formation until at least 50 percent of the pore volume of the part of the formation to be treated has been heated sufficiently to cause the hydrocarbon to liow toward the production well; l 3. stopping injection of steam of step (2) and injecting through a production well an oxygen-containing gas to create an in situ combustion front of hydrocarbon and thereby establishing a bidirectional flow; and

4. recovering hydrocarbon alternately through the production well and injection well respectively in the sequence ofsteps (2) and (3).

2. Method as claimed in claim l, wherein the oxygen-containing gas in step (3) is air. 

2. Method as claimed in claim 1, wherein the oxygen-containing gas in step (3) is air.
 2. injecting steam through one of the injection wells into the pores of the formation until at least 50 percent of the pore volume of the part of the formation to be treated has been heated sufficiently to cause the hydrocarbon to flow toward the production well;
 3. stopping injection of steam of step (2) and injecting through a production well an oxygen-containing gas to create an in situ combustion front of hydrocarbon and thereby establishing a bidirectional flow; and
 4. recovering hydrocarbon alternately through the production well and injection well respectively in the sequence of steps (2) and (3). 